As the semiconductor industry introduces new generations of integrated circuits (ICs) having higher performance and greater functionality, the density of the elements that form the ICs is increased, while the dimensions and spacing between components or elements of the ICs are reduced, which causes a variety of problems. For example, for any two adjacent conductive features, when the distance between the conductive features decreases, the resulting capacitance (parasitic capacitance) increases. The increased capacitance results in an increase of power consumption and an increase in the resistive-capacitive (RC) time constant, i.e., an increase of signal delays. The capacitance between two adjacent conductive features (e.g., metal wirings) is a function of the dielectric constant (k value) of an insulating material filled in the space between the conductive features (also, a function of a distance between the conductive features and a size of the side surfaces of the conductive features). Therefore, the continual improvement in semiconductor IC performance and functionality is dependent upon developing insulating (dielectric) materials with low k values. Since the substance with the lowest dielectric constant is air (k=1.0), air-gaps are formed to further reduce the effective k value of metal wiring layers.